The present disclosure relates to an information erasing device and an information erasing method where information recorded on a disk-shaped recording medium is erased, and in particular, which is appropriate to be applied when information recorded on a so-called recordable disk-shaped recording medium is erased.
As the technique for recording and reproducing digital data, for example, there is a data recording technique using an optical disc (including a magneto-optical disc) such as a CD (Compact Disc), a MD (Mini-Disc), a DVD (Digital Versatile Disc), a BD (Blu-ray Disc: registered trademark), or the like, as a recording medium. The optical disc is an all-inclusive term for disk-shaped recording media where reading out of recorded information is performed using the laser beam.
In the optical discs, for example, there are read-only types known as CDs, CD-ROMs, DVD-ROMs, and the like and types where user data is recordable known as MDs, CD-Rs, CD-RWs, DVD-Rs, DVD-RWs, DVD+RWs, DVD-RAMS, BD-Rs, BD-REs, and the like. The recordable type is able to record data using a magneto-optical recording method, phase change recording method, a dye film change recording method, or the like.
Out of the methods, the dye film change recording method and the like are referred to as so-called write-once recording methods, it is possible to perform data recording only once, and rewriting of data is not possible. The optical discs which correspond to the write-once recording methods are referred to as write-once type or recordable optical discs.
Here, with regard to write-once type optical discs, different to the case of optical discs where rewriting is possible, it is extremely difficult to overwrite and erase the recorded information. This is because, in the case of the write-once type optical discs, the recording film is damaged when the laser beam is radiated with the recording power to a target portion to erase the recorded information, and access to the vicinity thereof is extremely difficult. In other words, there may be cases where, since it is difficult to access the vicinity portion thereof, as a result, more data is lost than is necessary.
Due to the situation described above, data erasing in the write-once type optical discs is performed by dealing with the data as if it were erased by updating of management information using the file management system.
However, when using the method such as this, the data is not actually erased but still exists, and for example, it is possible to fraudulently obtain the data by performing reading out and the like which ignores the management information.
The situation becomes critical in a case where the data is, for example, related to private information or confidential information.
Here, the occurrence of a problem due to the erasing by overwriting as described previously is that all of the data which is the erasing target is overwritten. Therefore, in light of this, in regard to the erasing method of the write-once type optical discs, there is a way of thinking whereby all of the data which is the erasing target is not set as a target to be overwritten but only a partial sector of the data, which is sufficient so that data reproduction of the target sector is not possible, is overwritten and erased.
For example, in the disclosure disclosed in Japanese Unexamined Patent Application Publication No. 62-298072, a method is disclosed where, in a recordable optical disc where address information is recorded in a region of a narrow sector on a disc (address recording position 1a) and data is recorded in another region (information recording position 1b), reproduction is not possible with regard to information for which reproduction has been forbidden due to a dummy signal being recorded on the recording of the address information which corresponds to the information for which reproduction has been forbidden.
In this manner, through the reading out of the address information being not possible, it becomes possible for the reading out of the data which is the erasing target to be not possible without erasing by overwriting all of the data which is to be erased, and it is possible to simulate the erasing of all of the target data.